Constant velocity joint for vehicle

ABSTRACT

A constant velocity joint for a vehicle includes: an axle housing fixed to a knuckle by a hub bearing; a joint assembly inserted into an inner diameter portion of the axle housing and configured to transmit power from a shaft to the axle housing through a plurality of joint balls; an extension portion formed by deforming an end portion of the axle housing on an inward side of a vehicle body to extend in a radial direction of the axle housing so as to provide a pressing force to an inner race of the hub bearing in an axial direction of the axle housing; and a boot having one side surrounding an outer side of the extension portion to be coupled to the extension portion so as to form a restraining force between the extension portion and the boot in the axial direction.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to and the benefit of KoreanPatent Application No. 10-2020-0100708, filed on Aug. 11, 2020, theentire contents of which are incorporated herein by reference.

FIELD

The present disclosure relates to a structure of a constant velocityjoint transmitting power for driving a vehicle to a driving wheel.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

A constant velocity joint, which is a component, absorbing adisplacement between a differential and a driving wheel and transmittingpower to the driving wheel at a constant angular velocity, is configuredto be surrounded by a boot in an area where refraction is allowed,thereby preventing penetration of foreign substances from outside.

It is common that one side of the constant velocity joint is coupled tothe differential and the other side of the constant velocity joint isconnected to the driving wheel through a wheel hub, but the wheel hub isintegrally formed with the constant velocity joint in some cases.

The contents described as the related art have been provided only toassist in understanding the background of the present disclosure andshould not be considered as corresponding to the related art known tothose having ordinary skill in the art.

SUMMARY

The present disclosure provides a constant velocity joint for a vehiclein which a firmly coupled state of a boot can be easily secured and asealing function of the coupled boot can be excellently secured when theconstant velocity joint has a wheel hub that is integrally formedtherewith, thereby ultimately securing sufficient durability in arefraction portion of the constant velocity joint and moreover securelyassembling and maintaining the constant velocity joint in an excellentmanner.

According to one form of the present disclosure, a constant velocityjoint for a vehicle includes: an axle housing fixed to a knuckle by ahub bearing; a joint assembly inserted into an inner diameter portion ofthe axle housing and configured to transmit power from a shaft to theaxle housing through a plurality of joint balls; an extension portionextended from an end portion of the axle housing in a radial directionof the axle housing, wherein the extension portion is disposed on aninward side of a vehicle body of the vehicle and configured to provide apressing force to an inner race of the hub bearing in an axial directionof the axle housing; and a boot having one side that surrounds an outerside of the extension portion, is coupled to the extension portion, andforms a restraining force between the extension portion and the boot inthe axial direction.

The extension portion may have a protrusion protruding to have an outerdiameter greater than that of an end portion of the inner race on theinward side of the vehicle body.

The boot may have a first contact portion contacting an end portion ofthe extension portion on the inward side of the vehicle body, a secondcontact portion connected to the first contact portion and contacting anoutermost side of the protrusion, and a third contact portion connectedto the second contact portion and contacting the protrusion on anoutward side of the vehicle body to form an inner groove into which theprotrusion is inserted.

The protrusion may have a first inclined portion formed on the outwardside of the vehicle body to have an outer diameter gradually decreasingtoward the outward side of the vehicle body; and the third contactportion of the boot may be formed in parallel with the first inclinedportion.

The boot may have a first protruding end integrally formed to protrudelocally from the first contact portion toward the end portion of theextension portion on the inward side of the vehicle body.

The inner race may have a second inclined portion formed to have anouter diameter gradually increasing from an end portion thereof meetingthe extension portion toward the outward side of the vehicle body; andthe boot may have a fourth contact portion connected to the thirdcontact portion and formed in parallel with the second inclined portionto contact the second inclined portion.

The boot may have a second protruding end integrally formed to protrudelocally from the fourth contact portion toward the second inclinedportion of the inner race.

The inner race may have a first circumferential portion formed to have aconstant outer diameter from an end portion thereof meeting theextension portion toward the outward side of the vehicle body, and asecond circumferential portion connected to the first circumferentialportion and formed to have a constant outer diameter greater than thatof the first circumferential portion; and the boot may extend from thethird contact portion to surround both the first circumferential portionand the second circumferential portion.

An inner side surface of the boot surrounding the second circumferentialportion may form a third inclined portion having an inner diametergradually decreasing toward the outward side of the vehicle body.

The end portion of the axle housing on the inward side of the vehiclebody may be deformed to extend outwardly in the radial direction throughan orbital forming method, such that the extension portion has aprotrusion integrally formed to protrude to have an outer diametergreater than that of the end portion of the inner race on the inwardside of the vehicle body while pressing an end portion of the inner raceon the inward side of the vehicle body in the axial direction to fix theinner race.

A band may be fastened onto an outer side of the boot to press the boottoward the end portion of the inner race on the inward side of thevehicle body and the protrusion.

The boot may have a band fastening groove in the outer side thereof tofasten the band thereto; and when an axial-direction thickness of theextension portion is denoted as t, and a distance from an end portion ofthe extension portion on the inward side of the vehicle body to an endportion of the band fastening groove on the inward side of the vehiclebody is denoted as L, the end portion of the band fastening groove onthe inward side of the vehicle body may be located within a range of0≤L/t≤0.5.

When the outer diameter of the protrusion is denoted as d, and the outerdiameter of the end portion of the inner race on the inward side of thevehicle body is denoted as D1, the outer diameter d of the protrusionmay be within a range of 1.02≤d/D1≤1.05 to securely assemble the bootand inhibit or prevent the boot from escaping.

When an axial-direction width of the band is denoted as B and anaxial-direction thickness of the extension portion is denoted as t, thewidth B of the band is within a range of 0.3≤t/B≤1 to secure sufficientsealability.

According to another form of the present disclosure, a boot for aconstant velocity joint of a vehicle is formed to allow an extensionportion of an axle housing to be inserted thereinto to form arestraining force between the extension portion and the boot in an axialdirection of the axle housing. In particular, the axle housing receivespower from a shaft through a plurality of joint balls and is fixed to aknuckle by a hub bearing, the extension portion is formed by deforming apart of the axle housing, and the extension portion extends in a radialdirection of the axle housing and presses an inner race of the hubbearing in the axial direction to fix the inner race.

The boot may have a first contact portion contacting an end portion ofthe extension portion on an inward side of a vehicle body, a secondcontact portion connected to the first contact portion and contacting anoutermost side of a protrusion protruding such that the extensionportion has an outer diameter greater than that of an end portion of theinner race on the inward side of the vehicle body, and a third contactportion connected to the second contact portion and contacting theprotrusion on an outward side of the vehicle body.

When the protrusion has a first inclined portion formed on the outwardside of the vehicle body to have an outer diameter gradually decreasingtoward the outward side of the vehicle body, the third contact portionof the toot may be formed in parallel with the first inclined portion.

The boot may have a first protruding end integrally formed to protrudelocally from the first contact portion toward the end portion of theextension portion on the inward side of the vehicle body.

When the inner race has a second inclined portion formed to have anouter diameter gradually increasing from an end portion thereof meetingthe extension portion toward the outward side of the vehicle body, theboot may have a fourth contact portion connected to the third contactportion and formed in parallel with the second inclined portion tocontact the second inclined portion.

The boot may have a second protruding end integrally formed to protrudelocally from the fourth contact portion toward the second inclinedportion of the inner race.

When the inner race may have a first circumferential portion formed tohave a constant outer diameter from an end portion thereof meeting theextension portion toward the outward side of the vehicle body, and asecond circumferential portion connected to the first circumferentialportion and formed to have a constant outer diameter greater than thatof the first circumferential portion, the boot may extend from the thirdcontact portion to surround both the first circumferential portion andthe second circumferential portion.

An inner side surface of the boot surrounding the second circumferentialportion may form a third inclined portion having an inner diametergradually decreasing toward the outward side of the vehicle body.

The boot may have a band fastening groove in an outer side thereof tofasten a band thereto; and when an axial-direction thickness of theextension portion is denoted as t, and a distance from the end portionof the extension portion on the inward side of the vehicle body to anend portion of the band fastening groove on the inward side of thevehicle body is denoted as L, the end portion of the band fasteninggroove on the inward side of the vehicle body may be located within arange of 0≤L/t≤0.5.

When an axial-direction width of the band is denoted as B and anaxial-direction thickness of the extension portion is denoted as t, thewidth B of the band may be within a range of 0.3≤t/B≤1; and the bandfastening groove may be formed to have a width to accommodate the bandand restrain both ends of the band in the axial direction.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now bedescribed various forms thereof, given by way of example, referencebeing made to the accompanying drawings, in which:

FIG. 1 is a view illustrating a constant velocity joint for a vehicleaccording to a first form of the present disclosure;

FIG. 2 is a detailed view of a main portion of FIG. 1;

FIG. 3 is a view illustrating a constant velocity joint for a vehicleaccording to a second form of the present disclosure;

FIG. 4 is a view illustrating a constant velocity joint for a vehicleaccording to a third form of the present disclosure; and

FIG. 5 is a view illustrating a constant velocity joint for a vehicleaccording to a fourth form of the present disclosure.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

Referring to FIGS. 1 to 5, a constant velocity joint for a vehicle insome forms of the present disclosure includes in common: an axle housing7 having a plurality of hub bolts 1 and fixed to a knuckle 5 by a hubbearing 3; a joint assembly 13 inserted into an inner diameter portionof the axle housing 7 and configured to transmit power from a shaft 9 tothe axle housing 7 through a plurality of joint balls 11; an extensionportion 15 extended from an end portion of the axle housing 7 on aninward side of a vehicle body to extend in a radial direction of theaxle housing 7 such that the extension portion 15 provides a pressingforce to an inner race 3-1 of the hub bearing 3 in an axial direction ofthe axle housing 7; and a boot 17 having one side surrounding an outerside of the extension portion 15 to be coupled to the extension portion15 so as to form a restraining force between the extension portion 15and the boot 17 in the axial direction.

That is, the constant velocity joint according to the presentdisclosure, which is configured to convey the power transmitted from theshaft 9 to the axle housing 7 through the joint assembly 13, isconfigured as a hub-integrated constant velocity joint. Here, the axlehousing 7 is configured to allow the boot 17 to be coupled theretothrough the extension portion 15 formed by deforming a part of the axlehousing 7 to extend in the radial direction to fix the inner race 3-1 ofthe hub bearing 3.

The extension portion 15 has a protrusion 15-1 protruding to have anouter diameter greater than that of an end portion of the inner race 3-1on the inward side of the vehicle body.

That is, the protrusion 15-1 is a part of the extension portion 15,meaning a portion protruding outwardly beyond a portion pressing theinner race 3-1 in the axial direction in the extension portion 15 formedby deforming the end portion of the axle housing 7 on the inward side ofthe vehicle body to extend outwardly in the radial direction.

By deforming the end portion of the axle housing 7 on the inward side ofthe vehicle body to extend outwardly in the radial direction through anorbital forming method, the extension portion 15 is substantiallycapable of not only pressing the end portion of the inner race 3-1 onthe inward side of the vehicle body in the axial direction to fix theinner race 3-1 but also having the protrusion 15-1 protruding to have anouter diameter greater than that of the end portion of the inner race3-1 on the inward side of the vehicle body.

As described above, the boot 17 is fastened to the protrusion 15-1 toform a restraining force between the extension portion 15 and the boot17 in the axial direction.

Here, the axial direction means a direction of a rotation axis of theaxle housing 7, and the radial direction means a radial direction basedon the axial direction.

For reference, the axle housing 7 is fixed to the knuckle 5 in case of afront wheel, but may be fixed to a carrier in case of a rear wheel.

In addition, one side of the boot 17 is coupled to the extension portion15 of the axle housing 7, as described above, and the other side of theboot 17 is coupled to the shaft 9 to allow refraction between the shaft9 and the axle housing 7, while sealing and blocking such a refractionportion from the outside to function to inhibit or prevent penetrationof foreign substances.

The boot 17 has a first contact portion 19 contacting the end portion ofthe extension portion 15 on the inward side of the vehicle body, asecond contact portion 21 connected to the first contact portion 19 andcontacting an outermost side of the protrusion 15-1, and a third contactportion 23 connected to the second contact portion 21 and contacting theprotrusion 15-1 on an outward side of the vehicle body to form an innergroove 25 into which the protrusion 15-1 is inserted.

That is by inserting the protrusion 15-1 of the extension portion 15into the inner groove 25 formed by the first contact portion 19, thesecond contact portion 21 and the third contact portion 23 of the boot17, the restraining force is formed between the boot 17 and the axlehousing 7 in the axial direction.

Of course, a band 27 is coupled onto an outer side of the boot 17described above. The band 27 is coupled to press the boot 17 from theoutside toward the end portion of the inner race 3-1 on the inward sideof the vehicle body and the protrusion 15-1, thereby keeping the boot 17in a firmly coupled state.

The boot 17 has a band fastening groove 29 in the outer side thereof tofasten the band 27 thereto. When an axial-direction thickness of theextension portion 15 is denoted as t, and a distance from the endportion of the extension portion 15 on the inward side of the vehiclebody to an end portion of the band fastening groove 29 on the inwardside of the vehicle body is denoted as L, the end portion of the bandfastening groove 29 on the inward side of the vehicle body is locatedwithin a range of 023 L/t≤0.5.

That is, when the location of the end portion of the band fasteninggroove 29 on the inward side of the vehicle body is set as describedabove, an end portion of the band 27 on the inward side of the vehiclebody is resultantly located to firmly surround the outer side of theextension portion 15 to press the extension portion 15, which isadvantageous in seating the boot 17 and securing the sealability of theboot 17.

Meanwhile, when the outer diameter of the protrusion 15-1 is denoted asd, and the outer diameter of the end portion of the inner race 3-1 onthe inward side of the vehicle body is denoted as D1, the outer diameterd of the protrusion 15-1 is within a range of 1.02≤d/D1≤1.05.

This substantially limits a height at which the protrusion 15-1 of theextension portion 15 protrudes such that the protruding height of theprotrusion 15-1 is not too high, thereby securely assembling the boot17, and the protruding height of the protrusion 15-1 is not too low,thereby effectively inhibiting or preventing the boot 17 from escaping.

Meanwhile, when an axial-direction width of the band 27 is denoted as Band an axial-direction thickness of the extension portion 15 is denotedas t, the width B of the band 27 is within a range of 0.3≤t/B≤1.

This is to form the band 27 to have an axial-direction width greaterthan the axial-direction thickness of the extension portion 15, whilethe axial-direction width of the band 27 is not too great by about threetimes or more the axial-direction thickness of the extension portion 15,thereby not only securing the sufficient sealability of the boot 17 butalso easily handling and assembling the band 27.

Of course, the band fastening groove 29 is formed to have a width toaccommodate the band 27 and restrain both ends of the band 27 in theaxial direction.

Meanwhile, the protrusion 15-1 has a first inclined portion 31 formed onthe outward side of the vehicle body to have an outer diameter graduallydecreasing toward the outward side of the vehicle body, and the thirdcontact portion 23 of the boot 17 is formed in parallel with the firstinclined portion 31.

The first inclined portion 31 allows the third contact portion 23 of theboot 17 to be seated thereon to not only easily assemble the boot 17 butalso naturally induce a tightly coupled state between the boot 17 andthe protrusion 15-1 by the pressing force of the band 27, therebysecuring higher sealing performance.

The common configuration in all forms of the present disclosure has beendescribed above. Hereinafter, the remaining forms of the presentdisclosure will be described.

Referring to FIG. 3, a second form of the present disclosure is almostthe same as the first form as illustrated in FIG. 1, while beingdifferent in that the boot 17 has a first protruding end 33 integrallyformed to protrude locally from the first contact portion 19 toward theend portion of the extension portion 15 on the inward side of thevehicle body.

The first protruding end 33 is deformed to a compressed state betweenthe boot 17 and the end portion of the extension portion 15, therebyserving to form a more reliable sealing state.

A third form of the present disclosure, as illustrated in FIG. 4, isalmost, the same as the second form as illustrated in FIG. 3, whilebeing different in that: the inner race 3-1 has a second inclinedportion 35 formed to have an outer diameter gradually increasing from anend portion thereof meeting the extension portion 15 toward the outwardside of the vehicle body; and the boot 17 has a fourth contact portion37 connected to the third contact portion 23 and formed in parallel withthe second inclined portion 35 to contact the second inclined portion35.

In addition, the boot 17 has a second protruding end 39 integrallyformed to protrude locally from the fourth contact portion 37 toward thesecond inclined portion 35 of the inner race 3-1.

Accordingly, the boot 17 pressed by the band 27 toward the extensionportion 15 of the axle housing 7 is capable of securely sealing therefraction portion between the axle housing 7 and the shaft 9 in a morefaithful manner, based on a first sealing portion S1 formed by the firstcontact portion 19 and the end portion of the extension portion 15 onthe inward side of the vehicle body, a second sealing portion S2 formedby the second contact portion 21 and the outermost side of theprotrusion 15-1, a third sealing portion S3 formed by the third contactportion 23 and the first inclined portion 31, and a fourth sealingportion S4 formed by the fourth contact portion 37 and the secondinclined portion 35.

A fourth form of the present disclosure, as illustrated in FIG. 5, isalmost the same as the second form as shown in FIG. 3, while beingdifferent in that: the inner race 3-1 has a first circumferentialportion 41 formed to have a constant outer diameter from an end portionthereof meeting the extension portion 15 toward the outward side of thevehicle body, and a second circumferential portion 43 connected to thefirst circumferential portion 41 and formed to have a constant outerdiameter greater than that of the first circumferential portion 41; andthe boot 17 extends from the third contact portion 23 to surround boththe first circumferential portion 41 and the second circumferentialportion 43.

In addition, the boot 17 has a structure in which an inner side surfacethereof surrounding the second circumferential portion 43 forms a thirdinclined portion 45 having an inner diameter gradually decreasing towardthe outward side of the vehicle body.

In this case, the boot 17 is seated on the first circumferential part 41and the second circumferential part 43 on a side thereof facing theinner race 3-1 to implement a function of preventing penetration offoreign substances. In particular, the third inclined portion 45 of theboot 17 contacting the second circumferential portion 43 is structurallycapable of coupling an end portion of the boot 17 on the outward side ofthe vehicle body to the second circumferential portion 43 with a strongtightening force, thereby further reliably implementing the function ofpreventing penetration of foreign substances.

According to the present disclosure, in the constant velocity jointhaving a wheel hub that is integrally formed therewith, the firmlycoupled state of the boot can be easily secured and the sealing functionof the coupled boot can be excellently secured, thereby ultimatelysecuring sufficient durability in the refraction portion of the constantvelocity joint and moreover securely assembling and maintaining theconstant velocity joint in an excellent manner.

Although the present disclosure has been shown and described withrespect to specific forms, it will be apparent to those having ordinaryskill in the art that the present disclosure may be variously modifiedand altered without departing from the spirit and scope of the presentdisclosure.

What is claimed is:
 1. A constant velocity joint for a vehicle, theconstant velocity joint comprising: an axle housing fixed to a knuckleby a hub bearing; a joint assembly inserted into an inner diameterportion of the axle housing and configured to transmit power from ashaft to the axle housing through a plurality of joint balls; anextension portion extended from an end portion of the axle housing in aradial direction of the axle housing, wherein the extension portion isdisposed on an inward side of a vehicle body of the vehicle andconfigured to provide a pressing force to an inner race of the hubbearing in an axial direction of the axle housing; and a boot having oneside configured to: surround an outer side of the extension portion,coupled to the extension portion, and form a restraining force betweenthe extension portion and the boot in the axial direction.
 2. Theconstant velocity joint of claim 1, wherein the extension portion has aprotrusion having an outer diameter greater than a diameter of an endportion of the inner race on the inward side of the vehicle body.
 3. Theconstant velocity joint of claim 2, wherein the boot includes: a firstcontact portion configured to contact an end portion of the extensionportion on the inward side of the vehicle body, a second contact portionconnected to the first contact portion and configured to contact anoutermost side of the protrusion, and a third contact portion connectedto the second contact portion and configured to contact the protrusionon an outward side of the vehicle body to form an inner groove intowhich the protrusion is inserted.
 4. The constant velocity joint ofclaim 3, wherein the protrusion has a first inclined portion formed onthe outward side of the vehicle body, an outer diameter of the firstinclined portion gradually decreases toward the outward side of thevehicle body; and the third contact portion of the boot is formed inparallel with the first inclined portion.
 5. The constant velocity jointof claim 3, wherein the boot has a first protruding end protrudinglocally from the first contact portion toward the end portion of theextension portion on the inward side of the vehicle body.
 6. Theconstant velocity joint of claim 3, wherein the inner race has a secondinclined portion having an outer diameter gradually increasing from anend portion thereof and configured to meet the extension portion towardthe outward side of the vehicle body; and the boot has a fourth contactportion connected to the third contact portion and formed in parallelwith the second inclined portion to contact the second inclined portion.7. The constant velocity joint of claim 6, wherein the boot has a secondprotruding end protruding locally from the fourth contact portion towardthe second inclined portion of the inner race.
 8. The constant velocityjoint of claim 3, wherein the inner race includes: a firstcircumferential portion having a constant outer diameter from an endportion thereof and configured to meet the extension portion toward theoutward side of the vehicle body; and a second circumferential portionconnected to the first circumferential portion and configured to have aconstant outer diameter greater than the outer diameter of the firstcircumferential portion, and wherein the boot is configured to extendfrom the third contact portion and surround both the firstcircumferential portion and the second circumferential portion.
 9. Theconstant velocity joint of claim 8, wherein an inner side surface of theboot surrounding the second circumferential portion forms a thirdinclined portion having an inner diameter gradually decreasing towardthe outward side of the vehicle body.
 10. The constant, velocity jointof claim 1, wherein: the end portion of the axle rousing on the inwardside of the vehicle body is deformed to extend outwardly in the radialdirection, and the extension portion has a protrusion having an outerdiameter greater than an outer diameter of the end portion of the innerrace on the inward side of the vehicle body while pressing an endportion of the inner race on the inward side of the vehicle body in theaxial direction to fix the inner race.
 11. The constant velocity jointof claim 10, wherein a band is fastened onto an outer side of the bootand configured to press the boot toward the end portion of the innerrace on the inward side of the vehicle body and the protrusion.
 12. Theconstant velocity joint of claim 11, wherein: the boot has a bandfastening groove formed in the outer side thereof and configured tofasten the band thereto; and when an axial-direction thickness of theextension portion is denoted as “t”, and a distance from an end portionof the extension portion on the inward side of the vehicle body to anend portion of the band fastening groove on the inward side of thevehicle body is denoted as “L”, the end portion of the band fasteninggroove on the inward side of the vehicle body is located within a rangeof 0≤L/t≤0.5.
 13. The constant velocity joint of claim 11, wherein whenthe outer diameter of the protrusion is denoted as “d”, and the outerdiameter of the end portion of the inner race on the inward side of thevehicle body is denoted as “D1”, the outer diameter “d” of theprotrusion is within a range of 1.02≤d/D1≤1.05 to securely assemble theboot and inhibit the boot from escaping.
 14. The constant velocity jointof claim 11, wherein when an axial-direction width of the band isdenoted as “B”, and an axial-direction thickness of the extensionportion is denoted as “t”, the axial-direction width “B” of the band iswithin a range of 0.3≤t/B≤1 to secure sufficient sealability.
 15. A bootfor a constant velocity joint of a vehicle, the boot configured to allowan extension portion of an axle housing to be inserted thereto so as toform a restraining force between the extension portion and the boot inan axial direction of the axle housing, wherein: the axle housing isconfigured to receive power from a shaft through a plurality of jointballs and is fixed to a knuckle by a hub bearing, the extension portionis formed by deforming a part of the axle housing, and, and theextension portion extends in a radial direction of the axle housing andconfigured to press an inner race of the hub bearing in the axialdirection to fix the inner race.
 16. The boot of claim 15, wherein theboot includes: a first contact portion configured to contact an endportion of the extension portion on an inward side of a vehicle body, asecond contact portion connected to the first contact portion andconfigured to contact an outermost side of a protrusion of the extensionportion having an outer diameter greater than an outer diameter of anend portion of the inner race on the inward side of the vehicle body,and a third contact portion connected to the second contact portion andconfigured to contact the protrusion on an outward side of the vehiclebody.
 17. The boot of claim 16, wherein: the protrusion has a firstinclined portion formed on the outward side of the vehicle body, thefirst inclined portion is configured to have an outer diameter graduallydecreasing toward the outward side of the vehicle body, and the thirdcontact portion of the boot is formed in parallel with the firstinclined portion.
 18. The boot of claim 16, wherein the boot has a firstprotruding end protruding locally from the first contact portion towardthe end portion of the extension portion on the inward side of thevehicle body.
 19. The boot of claim 16, wherein: the inner race has asecond inclined portion having an outer diameter gradually increasingfrom an end portion thereof and configured to meet the extension portiontoward the outward side of the vehicle body, and the boot has a fourthcontact portion connected to the third contact portion and formed inparallel with the second inclined portion to contact the second inclinedportion.
 20. The boot of claim 19, wherein the boot has a secondprotruding end protruding locally from the fourth contact portion towardthe second inclined portion of the inner race.
 21. The boot of claim 16,wherein the inner race includes: a first circumferential portion havinga constant outer diameter and configured to meet the extension portiontoward the outward side of the vehicle body, and a secondcircumferential portion connected to the first circumferential portionand configured to have a constant outer diameter greater than theconstant outer diameter of the first circumferential portion, whereinthe boot is configured to extend from the third contact portion tosurround both the first circumferential portion and the secondcircumferential portion.
 22. The boot of claim 21, wherein an inner sidesurface of the boot surrounding the second circumferential portion formsa third inclined portion having an inner diameter gradually decreasingtoward the outward side of the vehicle body.
 23. The boot of claim 16,wherein the boot has a band fastening groove in an outer side thereof tofasten a band thereto; and when an axial-direction thickness of theextension portion is denoted as “t”, and a distance from the end portionof the extension portion on the inward side of the vehicle body to anend portion of the band fastening groove on the inward side of thevehicle body is denoted as “L”, the end portion of the band fasteninggroove on the inward side of the vehicle body is located within a rangeof 0≤L/t≤0.5.
 24. The boot of claim 23, wherein when an axial-directionwidth of the band is denoted as “B” and an axial-direction thickness ofthe extension portion is denoted as “t”, the axial-direction width “B”of the band is within a range of 0.3≤t/B≤1; and the band fasteninggroove is formed to have a width to accommodate the band and restrainboth ends of the band in the axial direction.